Method of cutting off laminate layers, eg a glass fibre or carbon-fibre laminate layer in the blade of a wind turbine

ABSTRACT

The invention relates to a method of cutting off laminate layers for use in a fiber-reinforced laminate object comprising a number of combined laminate layers, wherein, along a section of the at least one rim of the laminate layer, a tapering cut is performed through the thickness of the laminate layer, whereby the thickness of the laminate layer is reduced. Since not only the number of laminate layers, but also the thickness of the individual laminate layers are reduced, a laminate layer is accomplished that can be used in a laminate object, by which both the issues of areas rich in resin, air pockets and the risk of delamination are reduced. The invention also relates to a laminate layer for use in a fiber-reinforced laminate object comprising a number of combined laminate layers and a fiber-reinforced laminate object in the form of the blade of a wind turbine, wherein the blade of the wind turbine comprises a number of combined laminate layers.

This is a Continuation Application of U.S. patent application Ser. No.11/660,122, filed Apr. 9, 2007, which was filed under 35 U.S.C. 371 as anational stage of PCT/DK2005/000522 filed Aug. 10, 2005 which claimsbenefit under 35 USC 119 (e) from Danish Application No. PA 2004 01225,dated Aug. 13, 2004, the content of each of which is hereby incorporatedby reference in its entirety.

The invention relates to a method of cutting off laminate layers for usein a fibre-reinforced laminate object comprising a number of combinedlaminate layers. Moreover the invention relates to a laminate layer foruse in a fibre-reinforced laminate object comprising a number ofcombined laminate layers. Finally the invention also relates to afibre-reinforced laminate object in the form of the blade of a windturbine, wherein said blade of a wind turbine comprises a number ofcombined laminate layers.

Laminates are used for a wide variety of different objects, wherein alaminate object is composed of a number of combined laminate layers.

One example of an object composed of laminate layers is a glass-fibreobject, wherein, typically, a number of laminate layers in the form ofglass-fibre webs are arranged atop each other, and wherein the number oflaminate layers depends on the properties desired for the laminateobject. In connection with glass fibre objects resin is used for keepingthe layers together. The resin may be applied manually onto the laminatelayers by RTM (resin transfer moulding), VARTM (vacuum assisted resintransfer moulding) or any other suitable method. Alternatively the resinmay be applied onto the laminate layers prior to laying of the layers(Prepreg). In case it is desired to have an object that varies inthickness and changes from thick to more thin, the number of laminatelayers tapers off gradually across a certain length. The tapering offtakes place to avoid that notches show clearly and to reduce leaps instiffness through the laminate, which effects would otherwise reduce thestrength of the laminate.

It is a problem of such tapering off, however, that a tapered-off layermay loosen from the subjacent layer in the form of a delamination.Moreover, air pockets may form between the tapering-off and asuperjacent laminate layer which may in turn result in wrinkling of thelaminate. Both the issue of delamination and that of air pocketscontribute to a weakening of the strength of the laminate object.Moreover, when using eg the VARTM-method, areas rich in resin may formdue to the fact that, along the rim of the laminate layer, a channel isformed which may, during injection of resin, be caused to act as anundesired resin distribution channel. Those areas rich in resin areundesirable since the exothermal heat during the curing may adverselyinfluence the curing process and the laminate. In a worst-case scenariohardening strain cracks may occur in such resin-rich areas duringhardening of the resin.

EP 1 050 396 teaches a method of designing laminate objects and thedisclosure shows is a laminate object that varies in thickness, whereinthe variation in thickness is accomplished by the number of layers inthe laminate object being tapered off. However, it does not teach anysolution to the problem of delamination and the formation of air pocketsand resin-rich areas.

JP 0810528 teaches a tubular object composed of fibre-reinforcedlaminate layers. In order to reduce the risk of delamination, the tubeis chamfered along an edge at the one end. Here the object is chamferedfollowing construction of the object with laminate layers, which mayinvolve delamination between the layers in the chamfered region. It doesnot teach a solution to the problem of delamination in connection withthe variation in thickness and the formation of air pockets and areasrich in resin.

Thus, it is an object of the invention to provide a solution to theabove-mentioned problem.

This is accomplished by a method of cutting-off laminate layers for usein a fibre-reinforced laminate object comprising a number of combinedlaminate layers, wherein—at least along a section of the at least onerim of the laminate layer—a tapering cut is performed through thethickness of the laminate layer, thereby gradually reducing thethickness of the laminate layer. A fibre-reinforced laminate object isgenerally constructed by wrapping or laying layers of webs of materialatop each other. In case process methods are concerned wherein drylaminate layers are laid up, the invention relates to a method wherecutting is performed in laminate layers that are not yet impregnated.However, the invention may also be used for preimpregnated webs known bythe name of Prepreg. It is a common feature of all varieties (whetherdry or prepreg) that the tapering cut takes place on not-hardened fibrematerials. Since not only the number of laminate layers, but also thethickness of the individual laminate layers are reduced gradually, alaminate object is accomplished by which both the issues of areas richin resin, air pockets and the risk of delamination are reduceddramatically and the strength of the finished object is increased.

According to one embodiment the laminate layer is cut taperingly throughthe thickness, whereby the cut will be caused to form an acute angle toa subjacent laminate layer in a laminate object; and in one embodimentthe laminate layer is cut off taperingly in a concave curve. Accordingto yet an embodiment the laminate layer is cut off in a convex curve.The shape of the curve of the cut may be determined is on the basis ofstiffness conditions within the laminate layer and strains on thelaminate layer. Tests have shown that a tapering cut with an acute angleand/or a cut being cut in a concave or convex curve constitute(s) anadvantageous shape of curve, whereby the risk of delamination, areasrich in resin and air pockets is used considerably. The cuttingprocedure may take place either transversally and/or longitudinally ofthe laminate layers.

According to one embodiment the laminate layer is a fibre layer, egglass fibre, carbon fibre or other types of fibre for plasticscomposites. The fibre layer or the web may consist of eg short, cutfibres (chopped), of fibres laid primarily on one direction(unidirectional), or of fibres laid biaxially in two directions at someangle or other in relation to each other; however, in that embodimentthe fibre layer may also be woven, non-woven or stitched material. Itapplies in particular to such laminate layers that the problem ofdelamination is great and therefore a particularly effective solution tothe problem is accomplished by a tapering cut according to theinvention.

In a laboratory array for exercising the invention, the laminate layersare cut off by use of a tailor-made apparatus that cuts with afinger-cutting technique which is known is fra a cattle trimmer or anordinary hair trimmer. As it is, it has been found during work with thepresent invention that an entirely ordinary handheld hair trimmer maycut off the layers in a particularly convenient manner and enables avery accurate control of the cutting curve. However, obviously anindustrial apparatus for cutting off laminate layers in accordance withthe invention is required. Such apparatus may be constructed fromelements from eg the carpeting industry, wherein a suitable cuttingmethod/device is used for cutting patterns in loop and/or cut carpets.

Moreover the invention relates to a laminate layer for use in afibre-reinforced laminate object comprising a number of combinedlaminate layers, wherein the laminate layer along at least its one rimis cut off taperingly down through the thickness, thereby reducing thethickness of the laminate layer.

Moreover the invention relates to a fibre-reinforced laminate object inthe form of the blade of a wind turbine, wherein the blade of the windturbine comprises a number of combined laminate layers, wherein thelaminate layer is, along a section of at least its one rim, cut offtaperingly down through the thickness, whereby the thickness of thelaminate layer is reduced.

In the following the invention will be described in closer detail bymeans of figures that show exemplary embodiments of the invention:

FIG. 1 is a cross-sectional view of a laminate object structured fromlaminate layers in accordance with the prior art;

FIG. 2 is a cross-sectional view of a laminate object structured fromlaminate layers in accordance with the prior art, wherein delaminationhas occurred as a consequence of the tapering-off;

FIG. 3 is a cross-sectional view of a laminate layer according to theinvention;

FIG. 4A-4M is a cross-sectional view of laminate layers according to theinvention with different tapering and stepped cuts;

FIG. 5 is a cross-sectional view of a part of a laminate objectstructured from laminate layers in accordance with the invention;

FIG. 6 is a cross-sectional view of a portion of a laminate objectstructured from laminate layers in accordance with the invention, onwhich a top coat has been applied;

FIG. 7 is a cross-sectional view of a section of a laminate objectstructured from laminate layers in accordance with the invention,featuring an example of an internal tapering-off;

FIG. 8 is a cross-sectional view of a section of a laminate objectstructured from laminate layers in accordance with the invention,wherein the laminate layers are cut off taperingly as a convex curve;

FIGS. 9A-9C are cross-sectional views of sections of laminate objects,wherein the taperingly cut laminate layer may advantageously be used inconnection with joining to another object, eg in the context of repair;

FIG. 10 is a cross-sectional view of a laminate object, wherein thetaperingly cut laminate layer is used in connection with joints betweenlaminate layers;

FIG. 11 shows a laminate object in the form of the blade of a windturbine on which a tapered principal laminate is drawn.

FIGS. 12 and 13 show alternative cutting methods.

FIG. 1 is a cross-sectional view of a portion of a known laminate object101 comprising a number of combined laminate layers 103, wherein thelaminate object is made thinner by a change in the number of laminatelayers 103. In FIG. 1 the laminate object 101 initially comprises sixlaminate layers 103, and the number of laminate layers 103 is taperedoff gradually to three laminate layers 103, whereby the thickness of thelaminate object 101 is halved. The tapering-off takes place gradually isto avoid that notches are caused to show clearly, which would result ina weakening of the strength of the laminate object, but it may alsooccur to minimise the weight of the laminate in areas where the load onthe laminate object is not as high. FIG. 1 also illustrates an upperlayer 105 and the resin-rich areas and air pockets 107 that are formedbetween the upper layer 105 and the subjacent layers due to thetapering-off which may in turn result in wrinkling of the laminatesurface. In order to avoid these air pockets a surplus of resin isrequired, in case of glass fibre laminate is concerned, which is egvacuum injected underneath the upper layer 105 in order to keep thelaminate layers 103 together. A further problem associated with theknown laminate object is that a tapered-off layer may disengage from thesubjacent layer in the form of a delamination. Both the delaminationproblem, the resin-rich areas and the air pockets contribute to aweakening of the strength of the laminate object, and moreovercontribute to making the manufacture of laminate objects by eg vacuumprocesses, such as VARTM and the like, more difficult.

FIG. 2 is a cross-sectional view of a finished laminate (201) accordingto the prior art, wherein a delamination (203) in connection with thestepped tapering-off (205) is illustrated.

FIG. 3 illustrates a cross-section along a portion of a laminate layer.Here, in accordance with the invention and at the one end 303 along asection of the rim of the laminate layer 301, a tapering cut isperformed down through the thickness of the laminate layer 302. Herebythe thickness 302 of the laminate layer is gradually reduced. Byaccomplishing such tapering cutting-off of the laminate layer, wherebynot only the number of laminate layers, but also the thickness of theindividual laminate layers are reduced, laminate layers result that canbe used in a laminate object in which both the problems of areas rich inresin, that of air pockets and of delamination are reduced considerably.

A tapering cut is not to be construed to comprise merely a linearcutting-off illustrated in FIG. 3; rather it comprises any cut where thethickness of the laminate layer is cut off such that the thickness isreduced gradually or stepped. Examples of alternative cuts areillustrated in FIGS. 4A-4M showing how, in all cuts, the thickness ofthe laminate layer is cut off with different shapes of curves. One shapeof curve for the cut off can be determined eg on the basis of stiffnessconditions in the laminate layer and strains on the laminate layer.

FIG. 5 is a cross sectional view of a portion of a laminate object 501according to the invention comprising a number of combined laminatelayers 503 in accordance with the invention, wherein the laminate objectis made thinner by a change in the number of laminate layers 503.Initially, the laminate object 501 has six laminate layers 503, and thenumber of laminate layers 503 is tapered off gradually to three laminatelayers 503, whereby the thickness of the laminate object 501 is halved.In addition to a reduction in the number of layers, the thickness of theindividual laminate layer 503 is also reduced by a tapering cut of thelaminate layer being accomplished as shown in FIG. 3 rather than theabrupt cutting-off of the laminated layer shown in FIG. 1. In theexample shown in FIG. 5, the laminate layers were cut taperingly so asto form an acute angle 505 to a subjacent layer.

FIG. 6 is a cross-sectional view of a portion of a laminate objectcorresponding to the laminate object shown in FIG. 5, on top of which anupper layer 601 is applied. Owing to the tapering nature of the cuttingof the laminate layers, the occurrence of air pockets and areas 603 richin resin that are formed between the upper layer 601 and the subjacentlayers is minimised.

FIG. 7 is a cross-sectional view of a section of a laminate object 701with internal cut laminate layers 703 that are, as will appear, cutssituated between through-going laminate layers 705. It will appear fromthe Figure that by this variety of the invention, too, areas rich inresin and air pockets are avoided.

FIG. 8 is a cross-sectional view of a section of a laminate object 801according to the invention comprising a number of combined laminatelayers 803 in accordance with the invention. In addition to reducing thenumber of laminate layers 803 the thickness 805 of the individuallaminate layer is reduced, too, by the laminate layers being cut in aconvex curve.

FIGS. 9A-9C show cross-sectional views of portions of laminate objects,wherein the taperingly cut laminate layer may advantageously be used inconnection with the joining to another object, eg in connection withrepair procedures. Prior art is illustrated in FIG. 9A; therein it isdesired to combine a first section 901 with the laminate 903 comprisinga number of laminate layers 905. Again, the abrupt cuts of the laminatelayers may entail delamination and, in case an upper layer is concerned,areas rich in resin as well as air pockets may also follow. When cuttingof the layers is performed taperingly as shown in FIG. 9B or 9C suchproblems are vitiated.

FIG. 10 is a cross-sectional view of a portion of a laminate object1001, wherein the taperingly cut laminate layer can advantageously beused in connection with material transitions. Such transitions may beprovided with a view to a change of material or merely to continue alaminate layer 1003 with another laminate layer 1005. By cutting off thelaminate layers 1003 and 1005 in a tapering manner prior to assemblythereof, a larger gluing face between the layers is accomplished, andmoreover also the risk of the laminate layers delaminating in the jointsis reduced, which risk would have been higher had the laminate layersbeen cut off abruptly and not cut off taperingly or stepped.

FIG. 11 shows a laminate object in the form of a glass-fibre blade 1101of a wind turbine. The blade 1101 of the wind turbine is constructedfrom glass fibre laminate layers according to the invention, whereby ablade of increased strength is accomplished, where air pockets areminimised and the risk of delamination of the glass fibre laminateobject is minimised. FIG. 11 shows a part of the laminate layer of theblade illustrated as longitudinally extending panels, also called theprincipal laminate 1102 of the blade, by transversal lines 1103 thatindicate tapering in accordance with the invention.

If a laminate layer in the form of glass fibre or carbon fibre isconcerned, the cutting off process as such may be performed by means ofan apparatus that cuts using a finger cutting technique which is knowneg from a hair trimmer. Such apparatus may be structured from elementsfrom eg the carpeting industry, wherein a suitable cutting method/deviceis used for cutting patterns in loop and/or cut carpets. Alternativecutting methods may, as illustrated in FIGS. 12 and 13, consist eg inthat, in connection with the cutting of the layers 1201 by cutting unit1203, one mills or cuts the layers through, whereby a tapering cut isachieved by use of that process. In the figures the layers 1201 are cutoff by means of a rotating cutting unit 1203 which has a taperingprofile thereby cutting off the laminate layer 1201 such that it tapersoff. The profile of the cutting unit 1203, as shown in the figures, maytaper off to one or both sides, thereby accomplishing a tapering cut oftwo laminate layers in one cutting process. In one embodiment the layeris cut off gradually across three centimeters.

It will be understood that the invention as taught in the presentinvention with figures can be modified or changed while continuing to becomprised by the protective scope of the following claims.

The invention claimed is:
 1. A fiber reinforcement layer for use in afiber-reinforced laminate plastic composite comprising a number ofcombined laminate layers, wherein each fiber reinforcement layer along asection of at least one rim is tapered through the thickness of thefiber reinforcement layer, the fiber reinforcement layer comprising: alayer of glass fibers or carbon fibers, wherein the fiber reinforcementlayer is not-hardened, and wherein the fiber reinforcement layercomprises fibers which are laid primarily in one direction or the fibersare laid biaxially in two directions at some angle or other in relationto each other.
 2. The fiber reinforcement layer according to claim 1,wherein the fiber reinforcement layer is non-impregnated.
 3. The fiberreinforcement layer according to claim 1, wherein the fiberreinforcement layer is tapered at an end face of the fiber reinforcementlayer.
 4. A fiber-reinforced laminate object comprising a number ofcombined laminate layers, wherein at least one of said number ofcombined laminate layers is formed from a fiber reinforcement layeraccording to claim
 1. 5. A fiber-reinforced blade for a wind turbine,the fiber-reinforced blade comprising a number of combined laminatelayers, wherein at least one of said number of combined laminate layersis formed from a fiber reinforcement layer according to claim
 1. 6. Afiber reinforcement layer for use in a fiber-reinforced laminate plasticcomposite comprising a number of combined laminate layers, wherein eachfiber reinforcement layer along a section of at least one rim is taperedthrough the thickness of the fiber reinforcement layer, the fiberreinforcement layer comprising: a layer of glass fibers or carbonfibers, wherein the fiber reinforcement layer is not-hardened, whereinthe fiber reinforcement layer comprises fibers which are laid primarilyin one direction or the fibers are laid biaxially in two directions atsome angle or other in relation to each other, and wherein the fiberreinforcement layer is non-impregnated.